At present, most treatments that use chemical drugs or radiation for cancers or tumors affect tissue cells other than the target sites, and cause side effects such as aches, pyrexia and vomiting, and have therefore caused much suffering for patients. Further, secondary tumors resulting from the destruction of surrounding cells by drugs and radiation used in such treatments are becoming serious problems.
Accordingly, in recent years, increasing studies are being made on drugs for treatment of cancer and tumors with less side effects and on drug delivery systems, which allow drugs to be delivered directly to the target cancerous cells.
Among such recent findings, photodynamic treatment is a method wherein a target site is treated by incorporating into the body a compound that reacts with light such as ultraviolet light, visible light and infrared and irradiating the target site. Because the compound does not react without the irradiation of light, or at areas that are not irradiated, and only the cancerous cells at the target site are selectively destructed, the method has attracted much interest.
In such photodynamic treatment, photoreactive compounds that show high affinity to tumors and undergo photoexcitation in high yield are desired. Porphyrin compounds comprising a porphyrin ring are one type of photoreactive compounds known for photodynamic treatment. That is, porphyrin compounds react with ambient oxygen molecules by the irradiation of light, and through photoexcitation, convert them to singlet oxygen with high oxidative strength, which then oxidizes and destroys the surrounding cells.
Accordingly, oligomeric compounds having a porphyrin ring bound thereto and compounds comprising sugar chains, DNA, proteins or the like bonded to porphyrin have been proposed, and studies to accomplish higher cell recognition ability and tumor affinity are underway. However, many porphyrin compounds have been problematic in that they show high toxicity even without irradiation and often destroy cells other than those at the target site. Further, since the efficiency of the photoreaction and the affinity to tumor is low, it was necessary to inject high doses of the compound to the body, making the compounds far from desirable.
With respect to the foregoing problems, the present inventors have proposed, as compounds for photodynamic treatment, ionic porphyrin compounds which show low toxicity in vivo and destroy cancerous cells at the target site without attacking the surrounding cello (Japanese Patent Application 2000-17663). In practice, however, these compounds as dendrimers showed insufficient solubility in blood; in order to use the ionic porphyrin compounds as anticancer drugs in photodynamic treatment, it is required that these compounds show stability and efficiency in blood and are reliably delivered to the target site.
The invention of this application has been made under the foregoing circumstances, and upon solving the problems of the ordinary art, its object is to provide a polymeric micellar structure, which is capable of efficiently delivering the porphyrin compound for photodynamic treatment to the target cells, easy to use as a drug, and stable in water.